Infiltration of refractory metal base materials

ABSTRACT

This invention relates to a heavy metal body of a refractory metal containing material with a matrix of refractory metal containing alloy and to a method of making the same. The refractory metal containing material is preferably tungsten. The refractory metal containing alloy preferably includes molybdenum and a metal selected from the group consisting of iron, nickel, copper, cobalt, chromium, and mixtures thereof. The method of making the body includes the step of filling voids of a sintered refractory metal containing material skeleton, such as tungsten, with a molten alloy, such as a molybdenum-iron-nickel molten alloy. The resultant body has a fine grain particle size of refractory metal containing material of approximately the same particle size as the refractory metal containing material had before formation of the body, good ductility, negligible interaction between the alloy matrix and refractory metal containing material, and the skeleton experiences no harmful shrinkage during processing.

iinited States Patent Krock et a1.

[451 Dec. 30, 1975 [54] INFILTRATION 0F REFRACTORY METAL BASE MATERIALS[75] Inventors: Richard H. Krock, Weston; Jerome J. Pickett, Bedford,both of Mass.

[73] Assignee: P. R. Mallory & (30., Inc.,

Indianapolis, Ind.

[22] Filed: Oct. 23, 1973 [21] Appl. No.: 408,606

[52] US. Cl. 29/182.1; 75/200 [51] Int. CL 1322!? 1/00 [58] Field ofSearch 29/1821; 75/200 [56] References Cited UNITED STATES PATENTS3,305,324 2/1967 Krock et al. 29/182.l 3,338,687 8/1967 29/18213,340,022 9/1967 Zdanuk 29/182.1 3,353,933 11/1967 Zdanuk et a1...29/182.1 3,368,879 2/1968 Krock et al. 29/182.l 3,384,464 5/1968 Krocket al.. 29/182.1 3,407,048 10/1968 Krock et a1. 29/1821 3,440,043 4/1969Zdanuk et a1... 29/182.1 3,505,065 4/1970 Gwyn.... 29/l82.l

Primary ExaminerRichard D. Lovering Assistant Examiner--B. HuntAttorney, Agent, or FirmCharles W. Hoffmann; Robert F. Meyer; Donald W.Hanson [57] ABSTRACT This invention relates to a heavy metal body of arefractory metal containing material with a matrix of refractory metalcontaining alloy and to a method of making the same. The refractorymetal containing material is preferably tungsten. The refractory metalcontaining alloy preferably includes molybdenum and a metal selectedfrom the group consisting of iron, nickel, copper, cobalt, chromium, andmixtures thereof. The method of making the body includes the step offilling voids of a sintered refractory metal con taining materialskeleton, such as tungsten, with a molten alloy, such as amolybdenum-iron-nickel molten alloy. The resultant body has a fine grainparticle size of refractory metal containing material of approximatelythe same particle size as the refractory metal containing material hadbefore formation of the body, good ductility, negligible interactionbetween the alloy matrix and refractory metal containing material, andthe skeleton experiences no harmful shrinkage during processing.

US. Patent Dec. 30, 1975 INFILTRATION OF REFRACTORY METAL BASE MATERIALSThe present invention relates to metallurgy and more particularly toimproved refractory metal containing materials and to a method formaking the same.

Heavy refractory metal containing bodies have usefulness in operationswhere high density or high temperature resistant materials are required.These bodies also have good mechanical properties such as high tensilestrength, impact value, resistance to fracture under the application ofa bending stress and low thermal coefficients of expansion. The bodiesare used, for example, in aircraft counterbalances, radiation shielding,gyroscope inertia members, and high temperatures tooling components suchas die casting dies. When used in tooling operations, these bodies tendto minimize the problems normally associated with hot worked sheets suchas problems of thermal fatigue, heat checking, low hot hardness,soldering and oxidation.

Refractory metal containing bodies have a good combination of thermaland mechanical properties when produced by a liquid phase sinteringprocess as compared with production by conventional melting and castingtechniques. Liquid phase sintering (such as described in US. Pat. No.2,793,95 l) is a method utilizing powder metallurgy techniques whereinpowders such as refractory metal powders with lower melting point metalpowders which form an alloy, are formed into the desired body shape.During the heating step in liquid phase sintering, the molten alloydissolves an appreciable quantity of the refractory metal particles. Itis believed that the portion of the refractory metal thus dissolved isreprecipitated on undissolved refractory metal particles. This resultsin growth of grains of the main constituent (the refractory metal) andthe reduction or substantial elimination of voids in the skeleton by theformation of a matrix in the interstices between the grains of therefractory metal.

However, a drawback of the liquid phase sintering process is the harmfulshrinkage which tends to occur as a result of sintering of some shapesor bodies. Although simple shapes, such as square or round shapes, canbe made relatively easily, complex shapes such as die cavities can onlybe produced by extensive machining of the shapes. The problem ofshrinkage, recognized in U.S. Pat. Nos. 2,916,809 and 2,922,721, resultsin the need for complex calculations to compensate for shrinkage and forgood control of processing parameters to produce bodies within designtolerances, and, therefore, results in greater processing costs to yieldthe desired product.

It is, therefore, a primary feature of the present invention to provideheavy refractory metal containing bodies exhibiting a finer grainstructure than heavy refractory metal containing bodies typicallyproduced by a liquid phase sintering process. Another feature of theinvention is to provide heavy refractory metal containing bodies with aductility of about the same order of magnitude as heavy refractory metalcontaining bodies produced by a liquid phase sintering process. Anotherfeature of the present invention is to utilize infiltration techniquesin a method for the production of heavy refractory metal containingbodies. It is also a feature of the invention to hold shrinkage of thebody to a minimum during production processing of heavy refractory metalcontaining bodies and to hold to a minimum the amount of machiningrequired to produce the finished heavy refractory metal containing body.It is another feature of the present invention to produce refractorymetal containing bodies experiencing negligible interaction between therefractory metal containing material and the alloy matrix. Otherfeatures will be apparent from the following description and theappended claims. In the drawings:

FIG. 1 is a 4l0X photomicrograph of a tungsten base body with an alloymatrix of molybdenum, iron and nickel produced by a liquid phasesintering process; and

FIG. 2 is a 4l0X photomicrograph ofa tungsten base body with an alloymatrix of molybdenum, iron and nickel produced by the process of thisinvention.

The bodies of the present invention are composed of a refractory metalcontaining material as the major constituent, and an alloy matrix of arefractory metal and a metal or metals selected from the group of iron,nickel, copper, cobalt, and chromium. To be effective for hightemperature use, the body should include at least wt.% of the refractorymetal containing material. The refractory metal containing material ofthe invention need not be a pure elemental metal but can be inassociation with another element or elements or contain amounts ofimpurities which do not significantly affect properties of the heavymetal body. Carbides of the refractory metals are an example ofrefractory metal containing materials which are not pure metals that canbe used in providing the metal body.

Generally, the method of making the heavy metal body comprises the stepsof forming a porous sintered skeleton of refractory metal containingmaterial, filling voids of the skeleton with a molten alloy containing arefractory metal, and then solidifying the molten alloy to provide thedesired body. In the process, the refractory metal containing alloymatrix does not dissolve significant amounts of the refractory metalcontaining skeleton as might normally be expected, and, therefore, theresultant body has a finer grain structure than that of bodies producedby a liquid phase sinter process. An important advantage is realized inthat shrinkage is reduced significantly over liquid phase sintering thusallowing easier fabrication of complex body shapes. It is believed thatthe refractory metal present (such as molybdenum) in the infiltrantinhibits, to a significant degree, the dissolution of the refractorymetal (such as tungsten) of the skeleton by the infiltrant. Although themechanism by which such inhibition is accomplished is not understood, itis, perhaps, by saturation of the molten infiltrant alloy by the alreadypresent refractory metal (such as molybdenum).

More specifically, a compact of a refractory metal containing skeleton,such as tungsten, is formed by conventional powder metallurgy techniquesso as to have a density range of about 55 to about 70 vol.% oftheoretical density. A density of below about 55 vol.% of theoreticalusually yields a tungsten compact of insufficent mechanical strength tosupport itself or to withstand handling. Compacts having densities aboveabout 70 vol.% are difficult and costly to obtain in relation to theirvalue. In forming the porous skeleton, a suitable mold is utilized toform the refractory metal containing particles into the desired shape.The size of the particles of refractory metal containing material of thecompact may vary in accordance with the desired density of the finishedbody and with the desired pore size distribution in the skeleton. Choiceof the particles size of the compact also affects the final grain sizeof the body as the size remains approximately the same throughout theprocessing steps. A usual average particle size for the particles of thecompact is about 1 to about 10 microns. Compacting pressures or methodsof compacting can also be varied to yield different compact densities. Atypical compacting pressure for 10 micron tungsten powder is about 10tsi.

The compact of refractory metal containing material is presintered fromabout l000 to about l900C to provide a skeleton. The skeleton and therefractory metal containing alloy, prepared by a separate meltingoperation, are placed in close proximity. The combination is preheatedto about IOOO to about 1200C and then raised to normal sinteringtemperature, from about l350 to about l600C. At these temperatures, therefractory metal containing alloy melts and flows into the skeleton tofill void spaces of the skeleton yielding a body with an alloy matrixsubstantially surrounding the sintered particles of the refractory metalcontaining material. Temperatures associated with infiltration step arenot critical and infiltration can be accomplished over a fairly widetemperature range. Presintering temperatures can also be used tocontrol, to a degree, the porosity of the refractory metal skeleton. Theinfiltration step may take place in either a nonoxidizing atmosphere,such as hydrogen gas, or in a vacuum. After cooling, excess infiltrant,if any, is removed from the body.

The resultant body experiences negligible shrinkage from the initialdimensions of the porous skeleton and little, if any, distortion of thecontour of the skeleton is observed. The finished body includes arefractory metal containing skeleton surrounded by the refractory metalcontaining alloy matrix with void spaces of the skeleton filled by thealloy matrix. Examination of the grain structure reveals that there isnegligible interaction between the refractory metal containing particlesof the skeleton and the alloy matrix since the grain size of theskeleton particles remains approximately the same as the refractorymetal containing particles from which the skeleton is formed, muchsmaller than the grain size that is associated with liquid phasesintering of similar materials. Ductility and other properties of bodiesformed by the method of the present invention and by liquid phasesintering remain approximately the same however.

Referring now to FIG. 1 of the drawing, a photomicrograph of 410magnifications, a liquid phase sintered body of refractory metalcontaining material particles ll, tungsten particles, with an alloymatrix 12 of molybdenum-iron-nickel is shown. Note the largeglobule-like appearance of the tungsten particles 11. The globules oftungsten 1 1 are due to the interaction of the liquid phase (not shown)and refractory metal particles. The matrix alloy is in a weight ratio of2 parts molybdenum to 1 part iron to 2 parts nickel. The tungsten is 90wt.% of the total wt. of the body 10. In contrast, FIG. 2, aphotomicrograph of4l0 magnifications, shows a body with a grain-likestructure of tungsten particles 21 which experience little, if any,interaction between it and the infiltrant (an alloy 21 ofmolybdenum-iron-nickel in a 2:1:2 wt. ratio) during processing. Thetungsten grains 21 of the body 20 are substantially surrounded by thematrix 22 of the refractory metal containing alloy infiltrant. Thetungsten is about 75% by weight of the body 20. A comparison of thegrain structures of body 10 of FIG. 1 and that of body 20 of FIG. 2would seem to indicate that the body 10 would be significantly moreductile than body 20 as the grain structure is much more rounded in body10. Surprisingly enough, such is not the case however, as theductilities of the two bodies are of about the same order of magnitude.

The initial average tungsten particle size of the bodies shown in FIGS.1 and 2 is substantially the same. The process used to make the bodyshown in FIG. 2 results in an average tungsten particle sizesubstantially the same as the initial average tungsten particle size,whereas the process used to make the body shown in FIG. 1 results in anaverage tungsten particle size much greater than the initial tungstenaverage particle size.

Preferably the invention is utilized by employing tungsten particles asthe material for the skeleton, as tungsten apparently functions betterin the invention than other refractory metal containing materials. Morepreferably, tungsten is about to about 83 wt.% of the total wt. of thebody, and the refractory metal contain ing matrix is molybdenum, ironand nickel preferably in a weight ratio of about 2:112, respectively.The weight percent of molybdenum and nickel in the resultant body ispreferably about 6.8 wt.% to about 10 wt.% for each and for iron in theresultant body is about 3.4 wt.% to about 5 wt.%.

The following EXAMPLES are illustrative of the preparation of finegrained refractory metal containing bodies.

EXAMPLE I A sintered tungsten skeleton is infiltrated with an alloy ofabout 40 wt.% molybdenum, about 20 wt.% iron and about 40 wt.% nickel toprovide a body consisting essentially of about 75 wt.% W, about 10 wt.%Mo, about 5 wt.% Fe, and about 10 wt.% Ni.

A porous tungsten mass is compacted at about 10 tsi from tungstenparticles having an average particle size of about 3 to about 5 microns.The compact is presintered in hydrogen gas for about 4 hours at atemperature of about l460C to provide a skeleton. The density of thetungsten skeleton is about 58.5 vol.% theoretical. An infiltrant alloyof Mo-Fe-Ni in a wt. ratio of 221:2, respectively, is prepared byinduction melting. The required quantity of infiltrant, plus 15% volumeexcess is placed on the porous tungsten skeleton. The combination ofinfiltrant and skeleton is preheated to about ll0OC for about 1 hour inhydrogen gas and then heated to about l460C for about one-half hour inhydrogen gas to complete filling of voids of the skeleton withinfiltrant and then cooled. Excess infiltrant is removed. The body issound and exhibits negligible shrinkage and distortion. The bodyexhibits the following properties.

Density 14.7 g/cm Hardness R 36 2% yield strength ll9 ksi Ultimatetensile strength ksi Elongation 2.4%

The body has a fine grain structure as illustrated in FIG. 2.

EXAMPLE 11 A sintered tungsten skeleton is infiltrated with an alloy ofabout 40 wt.% tungsten, about 20 wt.% iron, and about 40 wt.% nickel toprovide a body consisting essentially of about 89.8 wt.% W, about 3.4wt.% Fe and about 6.8 wt.% Ni.

A porous tungsten mass is compacted at about tsi from tungsten particleshaving an average particle size of about 3 to 5 microns. The compact ispresintered in hydrogen for 4 hours at a temperature of about 1480C. Thedensity of the porous skeleton is about 68% theoretical by volume. Aninfiltrant of W-Fe-Ni in a wt. ratio of about 2:1:2 respectively isprepared by melting and is placed on the top of the skeleton with avolume excess. The skeleton is infiltrated by the infiltrant bypreheating to about 1100C for about 1 hour in hydrogen gas and thenheating to about 1450C for about one-half hour in hydrogen gas. Afterthe body is cooled, excess infiltrant is removed.

EXAMPLE III A sintered molybdenum skeleton is infiltrated with an alloyof about 40% molybdenum, about 40 wt.% nickel and about wt.% iron toprovide a body consisting essentially of about 85 wt.% Mo, about 10 wt.%Ni and about 5 wt.% Fe.

A porous molybdenum mass is compacted at about 12 tsi from molybdenumparticles having an average particle size of about 4 to 6 microns. Thecompact is presintered at about 1480C for about 4 hours. The infiltrantalloy of Mo-Ni-Fe in a wt. ratio of about 222:] respectively is preparedby induction melting and then placed on top of the porous skeleton. Theinfiltrant and the porous skeleton are preheated to about 1000C forabout 1 hour in hydrogen gas and then heated to about 1450C for about ahalf hour in hydrogen gas to infiltrate the voids of the skeleton andthen cooled. Excess infiltrant is then machined from the body.

EXAMPLE IV A sintered tungsten skeleton is infiltrated with an alloy ofabout 28.5 wt.% molybdenum, about 28.5 wt.% copper, about 28.5 wt.%nickel and about 14.5 wt.% iron to provide a body consisting essentiallyof 83 wt.% W, about 4.86 wt.% Mo, about 4.86 wt.% Cu, about 4.86 wt.% Niand about 2.42 wt.% Fe.

The operational steps and parameters are the same as in Example 1 exceptthe infiltrant alloy is of a different composition and the skeleton isof a different density.

EXAMPLE V A sintered tungsten skeleton is infiltrated with an alloy ofabout wt.% molybdenum, about 40 wt.%

- cobalt and about 20 wt.% iron to provide a body connsistingessentially of about 75 wt.% W, about 10 wt.% Mo, about 10 wt.% Co andabout 5 wt.% Fe.

The operational steps and parameters are the same as in Example I exceptthe infiltrant alloy is of a different composition.

Refractory metal is used here in the metallurgical sense to mean thegroup consisting of tantalum, molybdenum and tungsten.

Skeleton as used in this disclosure means a structure capable ofsupporting its own weight with interconnected void spaces throughout itsvolume.

Matrix is a substance or material in which another substance or materialis embedded.

The presence of small amounts of impurity elements is not believed toplay a critical role in the invention. It

should be understoodthat it is contemplated that minor amounts of otherelements can be added to the skeleton material or to the matrix materialor both and such practices are considered to be with the inventionherein described.

The present invention is not intended to be limited to the disclosureherein, and changes and modifications may be made by those skilled inthe art without departing from the spirit and scope of the presentinvention. Such modifications and variations are considered to be withinthe purview and the scope of the present invention and the appendedclaims.

We claim:

1. A body including refractory metal containing particles and a metalcontaining matrix, the refractory metal containing particles having anaverage particle size substantially equal to the average particle sizeof the refractory metal containing particles prior to the formation ofthe body, the body comprising as major weight constituent, refractorymetal containing particles, the refractory metal selected from the groupconsisting of tantalum, molybdenum and tungsten and as the minor weightconstituent, a metal containing matrix including a refractory metalselected from the group consisting of tantalum, molybdenum and tungstenand a metal selected from the group consisting of Ni, Fe, Co, Cu, Cr andcombinations thereof.

2. A body according to claim 1, wherein the refractory metal containingparticles are tungsten particles, preferably from -83 percent by weight.

3. A body according to claim 2, wherein the refractory metal of themetal containing matrix is molybdenum, preferably 40 wt.% of the matrix,and the other metals of the matrix are iron and nickel, preferably 20wt.% and 40 wt.% of the matrix respectively.

4. A method of making a body as claimed in claim 1, the body includingrefractory metal containing particles in a metal containing matrix, themethod comprising the steps of a. forming a porous shape of joinedrefractory metal containing particles,

b. filling voids of the shape with a molten metal containing matrixmaterial in such a manner that the average particle size of therefractory metal containing particles after filling voids with themolten matrix material is substantially the same as the average size ofthe refractory metal containing material prior to filling voids with themolten matrix material, the molten metal containing matrix materialincluding a refractory metal and a metal selected from the groupconsisting of Ni, Fe, Co, Cu, Cr or combinations thereof, and

c. solidifying the molten alloy to provide the body.

5. A method as claimed in claim 4, wherein the filling of the voids ofthe shape with the molten metal containing matrix material is done byinfiltration.

6. A method as claimed in claim 4, wherein the step of forming theporous shape of joined refractory metal containing particles includespressing of the particles.

7.'A method as claimed in claim 4, wherein the step of forming theporous shape of joined refractory metal containing particles includessintering of the particles.

8. A method as claimed in claim 4, wherein the refractory metalcontaining particles are tungsten particles and the molten metalcontaining matrix is molybdenum, nickel and iron, preferably in theweight ratio of 2:2:1 respectively.

9. A body according to claim 3, wherein the tungsten particles arepressed and sintered, infiltrated with an alloy of molybdenum, iron andnickel and then cooled.

UNITE!) siieirEs Pr-kIEN-T OFFICE CERTIFECATE 0F (ZORRECTION PATENT NO.929 424 DATED December 50, 1975 rNvENTOR(S) 1 Richard H. Krock andJerome J. Pickett It is certified that error appears in theabove-identified patent and that sard Letters Patent are herebycorrected as shown below.

Signed and Scaled this twenty-third Day of March 1976 sun A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParenlsand Trademarks UNHEE) 3%1' ETES PATENT OFFICE CETtFEQATE )F QURECTIONPATENT NO. I 3 929 424 DATED December 50, 1975 iNVENTORt I Richard H.Krock and Jerome J. Pickett It is certified that error appears in theabove-identified patent and that said Letters Patent 0 are herebycorrected as shown below.

- C01. 3, tine H insert "C" after 1000 0 ..Co]. 3, tine i5 insert "C"after 1000 C01. 3, tine i7 insert "C" after 1350 gigncd and Scaled this6 twenty-third of March 1976 [SEAL] Arrest.

b RUTH c. MASON C. MARSHALL DANN Arresting Officer (ommixsinnerofParenls and Trademarks

1. A BODY INCLUDING REFRACTORY METAL CONTAINING PARTICLES AND A METALCONTAINING MATRIX, THE REFRACTORY METAL CONTAINING PARTICLES HAVING ANAVERAGE PARTICLE SIZE SUBSTANTIALLY EQUAL TO THE AVERAGE PARTICLE SIZEOF THE REFRACTORY METAL CONTAINING PARTICLES PRIOR TO THE FORMATION OFTHE BODY, THE BODY COMPRISING AS MAJOR WEIGHT CONSTITUENT, REFRACTORYMETAL CONTAINING PARTICLES, THE REFRACTORY METAL SELECTED FROM THE GROUPCONSISTING OF TANTALUM, MOLYBDENUM AND TUNGSTEN AND AS THE MINOR WEIGHTCONSTITUENT, A METAL CONTAINING MATRIX INCLUDING A REFRACTORY METALSELECTED FROM THE GROUP CONSISTING OF TANTALUM, MOLYBDENUM AND TUNGSTENAND A METAL SELECTED FROM THE GROUP CONSISTING OF NI, FE, CO, CU, CR ANDCOMBINATIONS THEREOF.
 2. A body according to claim 1, wherein therefractory metal containing particles are tungsten particles, preferablyfrom 75-83 percent by weight.
 3. A body according to claim 2, whereinthe refractory metal of the metal containing matrix is molybdenum,preferably 40 wt.% of the matrix, and the other metals of the matrix areiron and nickel, preferably 20 wt.% and 40 wt.% of the matrixrespectively.
 4. A method of making a body as claimed in claim 1, thebody including refractory metal containing particles in a metalcontaining matrix, the method comprising the steps of a. forming aporous shape of joined refractory metal containing particles, b. fillingvoids of the shape with a molten metal containing matrix material insuch a manner that the average particle size of the refractory metalcontaining particles after filling voids with the molten matrix materialis substantially the same as the average size of the refractory metalcontaining material prior to filling voids with the molten matrixmaterial, the molten metal containing matrix material including arefractory metal and a metal selected from the group consisting of Ni,Fe, Co, Cu, Cr or combinations thereof, and c. solidifying the moltenalloy to provide the body.
 5. A method as claimed in claim 4, whereinthe filling of the voids of the shape with the molten metal containingmatrix material is done by infiltration.
 6. A method as claimed in claim4, wherein the step of forming the porous shape of joined refractorymetal containing particles includes pressing of the particles.
 7. Amethod as claimed in claim 4, wherein the step of forming the porousshape of joined refractory metal containing particles includes sinteringof the particles.
 8. A method as claimed in claim 4, wherein therefractory metal containing particles are tungsten particles and themolten metal containing matrix is molybdenum, nickel and iron,preferably in the weight ratio of 2:2:1 respectively.
 9. A bodyaccording to claim 3, wherein the tungsten particles are pressed andsintered, infiltrated with an alloy of molybdenum, iron and nickel andthen cooled.